Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: vicentebd on June 07, 2015, 10:46:52 pm
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I rewiring the preamp of 5E3, in parallel operation, as the Merlin book...keep the ECC81 maybe change for 12ax7
(http://s29.postimg.org/a9w5elm8z/parallel.jpg) (http://postimg.org/image/a9w5elm8z/)
I think this mode easy to do, and keep one channel original, This mod is useful for my case, Strat with Lace Sensor Gold PUs to be low output.
someone use this mod? there another mod, for extra gain?
Thanks vicente
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Marshall 1974 18 Watt amp normal channel uses that exact same circuit.
http://home.comcast.net/~seluckey/amps/18w/18w.pdf (http://home.comcast.net/~seluckey/amps/18w/18w.pdf)
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I know you said you'd like to keep one channel original but with a little switching you could wire one up in a cascode configuration for a pentode-esque gain stage (with gain to match!) that you could switch in and out.
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Thanks, for imput, with a little switching
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Is this configuration only suitable for v1 only? I just did it on V2 and I feel like it thinned the sound out rather than making it fat.
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Is this configuration only suitable for v1 only? I just did it on V2 and I feel like it thinned the sound out rather than making it fat.
What amp are you talking about??? The only amps mentioned so far in this thread are a Fender 5E3 and a Marshall 18W. V2 in both those amps is used for the phase inverter. Paralleling the V2 triodes in either of those amps is not applicable.
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A question which might help hesamadman:
On the lo input, should the cathode resistor still be halved to adjust for two triodes even though one grid is grounded?
The Matchless example halves the "typical" 1.5K cathode resistor and doubles the typical bypass cap. Merlin only drops the cathode resistor by 1/3, leaving single triode bias a bit cool if I'm not mistaken.
Chip
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While we're on the topic, I was thinking about this the other day.
What if I wanted to design a "parallel" input stage, tie the grids together, shared anode resistor, but set different bias points for each with separate cathode resistors and bypass caps? I know from Merlin's book if you're doing a typical parallel stage, you just double the current axis on the grid curves, but I don't think that would work here. Just think of them as two separate valves?
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While we're on the topic, I was thinking about this the other day.
What if I wanted to design a "parallel" input stage, tie the grids together, shared anode resistor, but set different bias points for each with separate cathode resistors and bypass caps? I know from Merlin's book if you're doing a typical parallel stage, you just double the current axis on the grid curves, but I don't think that would work here. Just think of them as two separate valves?
I don't see any problem with separate cathode resistor/cap networks. Actually, I think it might improve the Hi/Lo input arrangement. One of the AX-84 preamps has paralleled triodes with a blue LED under one and a red LED under the other. Ah, it's red and green:
http://ax84.com/static/corepreamps/Blues/AX84_Blues_Preamp_Schematic.pdf (http://ax84.com/static/corepreamps/Blues/AX84_Blues_Preamp_Schematic.pdf)
Cheers,
Chip
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> "parallel" input stage, ...shared anode resistor, ...separate cathode resistors
Does this count toward my grade?
Will it earn me a bonus in my paycheck?
If I know the answer, will the babes fall all over me?
I think you are just thinking-up hypothetical problems to amuse yourself.
First: if the idea is "more", why combine a "more" stage with a "less" stage? If they are very different, the more-stage will overwhelm the less stage. Probably not worth the 2 watts of heat. Two tubes in *cascade* will do much-much "more" than two tubes in one stage. And give more places to hang stuff. (Volume and tone-pots, tone-shapers, overload loss networks.)
Obviously you "can" compute the bias. Probably you can compute it on the curves. It is not "two separate valves" because the added constraint is that both plates must sit at the same voltage.
That amused me, for about 20 seconds.
The answer didn't come, and I didn't think it worth 21 seconds. Because even if you could predict "1.23mA, 0.678mA, 97V", what does that mean for THE MUSIC? Is it good for Polka? Ska? Funk? Bakersfield?
And why compute when you can BUILD? And build faster, since there isn't a cook-book analysis handy. 10 minutes of solder in an idle amp will not only tell you V and mA, it may give a fair start on discovering what The Sound is and how it might fit into THE MUSIC.
There is a cheap trick, especially for high-Mu triodes. You can do it on a matchbook cover. You can figure the approximate equivalent resistance from cathode resistor and Mu. You can then figure the approximate bias point from plate resistor and supply voltage. Knowing that both sections must get the =same= plate voltage, you can parallel the equivalent resistances, work out the plate voltage. Also total current. Now go back to the curves, plot the two cathode resistor lines, the estimated plate voltage, and read each plate current (they should sum to near the estimated total current).
But I do not see the point.
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I think you are just thinking-up hypothetical problems to amuse yourself.
Maybe. So? Something wrong with that? I build and experiment as time allows. When it doesn't, I think, read, and ask questions. Sorry if that annoys you.
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Pinkphiloyd,
Don't take PRR the wrong way. From what I've seen, He's extremely smart (scary sometimes), and usually sounds a little annoyed at us non-electrical engineers. But he's always quick to help and his insights (although often over my head) are invaluable.
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Sorry if that annoys you.
He's not annoyed. That's just part of his humor.
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Sorry if that annoys you.
He's not annoyed. That's just part of his humor.
Them New Englanders. :icon_biggrin:
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Fair enough. Tone, in writing, is easily misinterpreted. I apologize.
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If I was annoyed, I wouldn't have given you several ways to go further with your search.
I am sorry if you felt that a detailed answer to your question was a personal attack.
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If I was annoyed, I wouldn't have given you several ways to go further with your search.
I am sorry if you felt that a detailed answer to your question was a personal attack.
I don't think "personal attack" is the best description. Some of your remarks did strike me as grossly condescending, but I have since been informed that this merely your posting style. So, again, I apologize that I misconstrued your initial response.
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grossly condescending
that's when you burn the midnight oil, futilely trying to glean the wisdom imparted on you :icon_biggrin: